1. Technical Field
The present invention relates to an integrated circuit, particularly to the activation of a circuit block in an electronic circuit, and to a method for activating a switched-off circuit block to minimize leakage currents.
2. Background Information
To reduce these leakage currents there is the possibility of intermittently turning off circuit blocks of the electronic circuit which are not required, for example of a digital CMOS circuit. If the circuit block is to be brought out of the deactivated state and back into the activated state, its inner capacitors which were discharged in the deactivated state must be charged again, and this leads to an intensified flow of current. Strong, uncontrolled switching activities (glitches), which, in addition to the charging current, cause the flow of current in the supply lines, also occur during the reactivation process. As a result the total current when switching on a circuit block is briefly very high, and this leads to a noticeable voltage drop on the voltage supply network. Consequently, the operating voltage drops, which is seen by the other, adjacent circuit blocks. The briefly reduced voltage supply leads to lower current flows, and this leads to a brief reduction in the switching speed. This reduction in the switching speed can lead to malfunctions as a result of timing infringements in the critical path, and this can lead to malfunctions or to a system failure. However, a loss of data, which is stored in the flip-flops of the blocks, is not anticipated for a sensibly dimensioned supply network.
The voltage drop caused by the reactivation of a circuit block cannot be avoided by regulation of the voltage supply as the switch-on peaks have much lower time constants than the voltage regulator. A voltage regulator would be too sluggish to support these power fluctuations.
While capacitive buffering of the voltage supply is possible in principle, very large capacitors would be required on the electronic circuit's chip for this purpose, the area requirement of which is impractical.
A further problem in this connection is that during operation with turning off circuit blocks, conventionally it must be identified early when which circuit block is required. However, when turning off a small section the situation can occur where only one system cycle is identified in advance, before the associated circuit block is required again. There is therefore no more time in which to activate this block in discrete steps, so it must be estimated in advance when the function block will be required. This can also frequently lead to misactivations, whereby stray power is also generated.
Consequently a need exists to provide a circuit arrangement with which it is possible to activate circuit blocks in short periods without adjacent circuit blocks being adversely affected.